Anthony Cate¹; ¹Roanoke College

INTRODUCTION: Perception of the 2D outlines shapes of concave and convex 3D forms relies on qualitatively different visual features, which suggests that there may be two distinct pathways for perceiving 3D shape (Cate & Behrmann, 2010). This study investigated whether the basic shape features of concavities and convexities have different spatial extents, based on the idea that visual crowding is related to isolation field size (e.g. Pelli et al., 2004). METHODS: Participants with normal or corrected vision identified capital letters (stroke width 1.5˚) presented within random dot stereograms on a CRT monitor synchronized with LCD shutter glasses. The background portion of each stereogram filled the display, and had a uniform disparity of either 6' crossed, 6' uncrossed, or 0. 3D letters with either convex or concave depth structure were produced by creating regions with smoothly changing disparities that appeared either nearer or farther than the background. These relative disparity differences extended to 6'. On each trial, an array of three vertically arranged letters appeared briefly (150 ms) at 11˚ eccentricity, randomly to the left or right of fixation. Participants identified the middle letter. The two flanker letters were separated from this target either by a tight spacing that produced crowding (5.5˚), or by a loose spacing that did not (16.5˚), as established by a previous study (Cate & Hartman, VSS 2016). Visual crowding was as measured the difference in correct identifications for the loose minus tight spacing conditions. RESULTS: Crowding was significantly higher in the right hemifield for concave letters, and in the left hemifield for convex letters. CONCLUSION: This may suggest that concave and convex 3D forms recruit shape perception processes that differ according to the parts-based and holistic processing distinction attributed to the left and right cerebral hemispheres (e.g. Robertson & Lamb, 1991).